Research Highlights Biogas Threat to Gas Regulators

Failure to adequately remove sulphur from biogas poses a threat to commercial and industrial gas regulators, reports world leading gas meter and regulator diaphragm maker, Metflex. Research carried out by Metflex, in collaboration with independent test laboratories, has shown that levels of hydrogen sulphide as little as 1% can significantly reduce the regulator’s rubber diaphragm service life.

Biogas production buildings and windmillRubber diaphragms are widely used in gas meters and commercial and industrial gas regulators. Traditionally made from either NBR (nitrile butadiene rubber) or ECO (Epichlorohydrin Rubber), the diaphragms are used to ensure continuous flow and regulate gas flow respectively. A regulator diaphragm exposed to natural gas can expect to flex through over several million cycles over 5 years operational life.

Biogas generated through either anaerobic digestion or fermentation of biodegradable materials, comprises typically 55-65% methane, 35-45% carbon dioxide, 0.5-1.0% hydrogen sulphide and traces of water vapor. Long-term exposure to sulphur can cause the diaphragm to harden, leading to cracking and premature failure. Flex testing has shown a reduction of up to 70% in diaphragm service life due to sulphur.

“Rubber diaphragms for gas meters and regulators are designed for natural gas where levels of sulphur are negligible,” says Chris Greenwood, sales director, Metflex Ltd.

“With biogas, the energy industry is faced with either investing in more sophisticated gas scrubbing equipment or switching to a rubber with greater resistance to sulphur.”

HNBR – biogas resistant

Metflex research has identified a peroxide-cured, hydrogenated NBR (HNBR) as the most cost-effective alternative to NBR. Hydrogenation eliminates the NBR’s structural ‘double bond’ attacked by sulphur.

“HNBR has the same mechanical properties as NBR but with greater chemical resistance. Tests of HNBR diaphragms exposed to biogas have shown a flex life more in line with that expected with natural gas,” Chris Greenwood notes.

Metflex is the clear technology leader in the manufacture of rubber diaphragms for consumer, commercial and industrial gas meters and regulators. The company’s Dispersed Fibre Technology (DFT) enables production of ultra-thin, precision moulded diaphragms that have set the standard for performance and longevity within the global gas meter industry.

For more information on Metflex call +44 (0)1254 884171, visit the web site www.metflex.co.uk or email sales@metflex.co.uk

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